In recent years there has been growing interest in organic electronic (OE) devices, for example organic field effect transistors (OFET) for use in backplanes of display devices or logic capable circuits, and organic photovoltaic (OPV) devices. A conventional OFET has a gate electrode, a gate insulator layer made of a dielectric material (also referred to as “dielectric” or “gate dielectric”), source and drain electrodes, a semiconducting layer made of an organic semiconductor (OSC) material, and typically a passivation layer on top of the aforementioned layers to provide protection against environmental influence or against damage from subsequent device manufacturing steps.
For OE devices solution processable OSC layers are especially desired. The OSC materials should be solution based and should be suitable for solution based deposition methods such as spin-coating, slot-die coating and doctor blade coating, or wider area printing methods such as flexo, gravure, and screen printing. Key requirements for OSC materials used in such solution processed layers are orthogonality of the OSC solvent towards the underlying device layer, and good adhesion of the OSC to the device layers provided above and below the OSC layer, such as gate dielectric or passivation layers.
Parylene (poly(p-xylylene) is a dielectric material that is commonly used in dielectric or passivation layers of OE devices such as OFETs. Parylene is a commercially available dielectric which polymerizes when being deposited on a substrate from a vaporized p-xylylene monomer. The advantage of Parylene is its relatively simple processing, resulting in a highly pure and homogeneous thin film, which is an excellent chemical barrier, both thermally stable and UV stable.
However, the adhesion of Parylene to the commonly used solution processable OSC compositions is often very low.
Thus it would be desirable to provide solution processable OSC formulations for the preparation of OSC layers in OE devices, which show improved adhesion to a Parylene layer as used in dielectric or passivation layers of such devices.